1. Field of the Invention
The present invention relates to a lens barrel for an imaging apparatus incorporated in a small electronic device such as a portable terminal device. More specifically, the present invention related to a lens barrel for an imaging apparatus, a camera module, and an imaging apparatus that use a voice coil motor in a focus drive mechanism.
2. Description of the Related Art
Most imaging apparatuses installed in cellular phone terminals are equipped with an auto-focus function. In order to use the auto-focus function, it is necessary to move a group of optical lenses inside in an optical-axis direction. As a mechanism that drives the group of lenses, voice coil motors in which a drive coil or a magnet is moved through an electromagnetic induction phenomenon caused by a magnetic circuit are widely used.
In many of the voice coil motors in which the drive coil is movable, the drive coil is fixed to the outer peripheral portion of a lens holding member using an adhesive or the like for assembly. Also, the magnet is attached to a fixed portion provided outwardly of the drive coil to face the drive coil.
Thus, the size of the magnet significantly affects the external size of the lens barrel. Therefore, in view of the circumstances in which it is desirable to reduce the size of the entire lens barrel, it may be difficult to secure a space for the magnet. It may also be difficult to secure a space for a yoke, which is used together with the magnet. Reducing the size of the magnet to secure a space for the yoke may reduce the thrust for the lens holding member provided on the side of a movable portion.
Further, it may be necessary that in the case where the cellular phone or the like equipped with the imaging apparatus is subjected to a drop impact, for example, the magnet should not come out of a predetermined position to be caught into the drive coil of the movable portion.
Japanese Unexamined Patent Application Publication No. 2007-108595 is an example of the related art.